A known driver monitor system is configured to monitor a driver of a vehicle in order to detect the direction of the driver's face, the opening state of driver's eyes, and the like FIG. 13 shows an overview of a driver monitor system 100 according to a prior art. The driver monitor system 100 includes a projector 102 configured to project light, such as near-infrared light, to a projection region 101 in order to image a driver's face located in the projection region 101 clearly regardless of day or night. The driver monitor system 100 further includes a camera 103 configured to photograph an image of the projection region 101 projected with light from the projector 102. An imaging control unit 104 controls a gain, an exposure time (exposure timing), and the like of the camera 103. In addition, a projection control unit 105 controls a light strength, a projection timing, and the like of the projector 102. The photographic image captured by the camera 103 is sent to an image processing unit 106. The image processing unit 106 implements a predetermined image processing on the photographic image thereby to detect a face region corresponding to the driver's face. Thus, the information on the detected driver's face region is utilized by various systems 107 such as a system for avoiding drowsy driving, a system for avoiding inattentive driving, and the like. Specifically, the various systems 107 detect the direction of the driver's face, the opening state of the driver's eyes, and the like, according to, for example, the face region. The various systems 107 further implement a processing, such as a warning processing, according to the detection result.
As described above, a conventional face imaging system includes a projector (projection unit) configured to project light in a predetermined projection region, in which a driver's face is located, and a camera (imaging unit) configured to photograph an image in the projection region (see, for example, publication of Japanese patent No. 4419609).
It is noted that, in the conventional face imaging system, the projector continues projection of light even when a face of a user, such as a driver, does not exist in the projection region or even when the face existing in the projection region cannot be detected. Therefore, in such a conventional system, when a user looks into a projector suddenly or when a user approaches the projector too closely, the light from the projector may cause eyestrain in the user's eyes. In particular, pupils of the user's eyes hardly expand and contract when projected with near-infrared light from the projector, compared with a case when being projected with visible light. Therefore, the user's eyes may cause severe eyestrain when being projected with near-infrared light.